Internal mold release agents used in the production of molded polyurethane and polyurea products are known. Many of the known internal release agents are based at least in part on fatty acid esters. Typical of such release agents are those described in U.S. Pat. Nos. 3,726,952, 3,925,527, 4,058,492, 4,098,731, 4,201,847, 4,254,228, 4,868,224 and 4,954,537, and British Patent 1,365,215.
U.S. Pat. Nos. 4,519,965 and 4,581,386 describe the use of zinc carboxylates as internal mold release agents for the production of molded polyurethane and/or polyurea elastomers.
More recently developed internal mold release agents are also acidic in nature. Typical of such release agents are those based on polymerized fatty acids, lower alkyl aceto-acetates, and esters of saturated/unsaturated monocarboxylic acid mixtures (U.S. application Ser. Nos. 07/698,069, 07/660,759, and 07/697,153, filed on Apr. 22, 1991, Feb. 25, 1991, and May 8, 1991, respectively).
One recurring problem with all of these acidic internal release agents is that they generally cause an increase in the reactivity of the system, while at the same time causing a reduction in the green strength of the resultant molded product. Green strength is a measure (usually subjective) of the ability of a material to be demolded. Green strength is significantly affected by temperature, mold residence time, and part configuration (i.e., simple shapes demold more easily than complex ones), as well as by polymer recipe. U.S. Pat. No. 4,111,861 discloses acidic additives to facilitate mold release of a RIM system and recognized the increased reactivity caused by such additives (note column 3, lines 30 ff). The reference overcame the reactivity problem by combining the acidic additive with a polar metal compound.